The present invention relates to a sub-millimeter wavelength imaging device and particularly but not exclusively to an ambient temperature camera using either single or multiple heterodyne detectors.
The terahertz electromagnetic spectrum extends over a range of frequencies where radio waves and optical waves merge and consequently the detection of terahertz radiation utilises a mixture of optical and radio wave technology. As a result of the dimensions of the individual components required to image at terahertz frequencies, the cost of terahertz imaging systems has generally been prohibitive.
However, terahertz frequencies have long been recognised as potentially extremely useful frequencies for imaging purposes as many materials which are opaque in the visible region of the spectrum become transparent to terahertz waves. In particular imagers at terahertz frequencies are suitable for imaging the Earth's surface as most weather conditions such as fog are transparent to terahertz waves. This also makes a terahertz imager a potentially useful imaging device when flying a plane or driving a land vehicle in bad weather, for example. The transparency of many materials to terahertz frequencies has also been identified as a useful tool for security purposes. Most notably clothing becomes transparent at these frequencies enabling hidden weapons worn under clothing to be seen clearly and for spotting people hidden in canvas sided trucks and lorries. Furthermore, In view of the fact that human bodies radiate at these frequencies, terahertz radiation has also been identified as a potentially powerful diagnostic tool for example in the early detection of skin cancers. Also, applications of terahertz imaging in the chemical and food industries have been identified, for example in the detection of one or more constituents each having different transmissive/reflective properties at these frequencies.